There are many conventionally known methods for sensitizing silver halide photographic light-sensitive materials, which include the spectral sensitization by use of sensitizing dyes; the noble metal sensitization by use of salts of noble metals such as gold, platinum, iridium, etc.; the sulfur sensitization by use of active gelatin, sodium thiosulfate, thioacetamide, allyl-isothiourea, etc.; the selenium sensitization by use of colloidal selenium, selenourea, etc.; the reduction sensitization by use of a stannous salt, polyamine, hydrazine derivative, etc.: the development acceleration by use of a salt of nitrogen-, phosphorus- or sulfur-polyonium, or of a polyalkylene glycol; or the like. In the actual photographic industry, such sensitizing techniques are used in arbitrary combination according to purposes to manufacture an objective silver halide photographic material, but any techniques capable of adequately meeting the demand for the long-term preservability have not yet been established. So, attempts have now been exerted to make the light-sensitive material still further highly sensitive by additionally applying a novel sensitizing technique to the silver halide photographic material that has been sensitized by combining some of these well-known sensitizing techniques or by employing such the novel sensitizing technique alone. However, the improvement is still not sufficient.
On the other hand, regarding the technique on silver halide grains for raising the photographic speed of a silver halide emulsion, there are those monodisperse-type and tabular-type core/shell emulsions as disclosed in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) Nos. 138538/1985, 143331/1985, U.S. Pat. No. 4,444,877, Japanese Patent O.P.I. Publication Nos. 99433/1984 and 35726/1985. The technique for these emulsions is a device made in the latent image forming process so that the light that has been absorbed into the inside of a silver halide grain is efficiently transformed into a development speck. The technique, however, has been demanded yet to be improved on the emulsion's long-term preservability.